Typescript DID Resolver

This library is intended as a simple common interface for javascript applications to resolve DID documents from Decentralized Identifiers (DIDs).

This is intended to support the proposed Decentralized Identifiers spec from the W3C Credentials Community Group.

The library does not implement any specific DID method, but allows DID method implementors to release npm packages that applications can add.

Configure Resolver object

You are now required to preconfigure a resolver during instantiation. The Resolver constructor expects a registry of methods mapped to a resolver function. For example:

{ethr: resolve,web: resolve}

Each method resolver should expose a function called getResolver which will return an object containing one of these key/value pairs. Then you can flatten them into one object to pass into the Resolver constructor.

import{Resolver}from'did-resolver'importethrfrom'ethr-did-resolver'importwebfrom'web-did-resolver'importsovfrom'sov-did-resolver'//returns an object of { methodName: resolveFunction}ethrResolver=ethr.getResolver()webResolver=web.getResolver()//If you are using multiple methods you need to flatten them into one objectconstresolver=newResolver({
...ethrResolver,
...webResolver,})//If you are using one method you can simply pass the result of getResolver( into the constructorconstresolver=newResolver(ethrResolver)

Using legacy DID Method resolvers

DID Method resolvers created before version 3.0.0 of this library can be used as legacy resolvers.

import{Resolver}from'did-resolver'importwebfrom'web-did-resolver'importsovfrom'sov-did-resolver'//returns an object of { methodName: resolveFunction}webResolver=web.getResolver()sovResolver=sov.getResolver()//If you are using multiple methods you need to flatten them into one objectconstresolver=newResolver({},{legacyResolvers: {
...webResolver,
...sovResolver,}})//If you are using one method you can simply pass the result of getResolver( into the constructorconstresolver=newResolver(ethrResolver)

Resolving a DID document

The resolver presents a simple resolve() function that returns a ES6 Promise returning the DID document.

resolver.resolve('did:ethr:0xF3beAC30C498D9E26865F34fCAa57dBB935b0D74/some/path#fragment=123').then(doc=>console.log)// You can also use ES7 async/await syntaxconstdoc=awaitresolver.resolve('did:ethr:0xF3beAC30C498D9E26865F34fCAa57dBB935b0D74/some/path#fragment=123')

Caching

Resolving DID Documents can be expensive. It is in most cases best to cache DID documents. Caching has to be specifically enabled using the cache parameter

The built-in cache uses a Map, but does not have an automatic TTL, so entries don't expire. This is fine in most web, mobile and serverless contexts. If you run a long-running process you may want to use an existing configurable caching system.

The built-in Cache can be enabled by passing in a true value to the constructor:

constresolver=newDIDResolver({
ethr,
web
},{cache: true})

Here is an example using js-cache which has not been tested.

varcache=require('js-cache')constcustomCache : DIDCache=(parsed,resolve)=>{// DID spec requires to not cache if no-cache param is setif(parsed.params&&parsed.params['no-cache']==='true')returnawaitresolve()constcached=cache.get(parsed.didUrl)if(cached!==undefined)returncachedconstdoc=awaitresolve()cache.set(parsed,doc,60000)returndoc}constresolver=newDIDResolver({
ethr,
web
},{cache: customCache})

Implementing a DID method

Each DID method will have its own methods for looking up an identifier on its respective blockchain or other decentralized storage mechanism.

To avoid misconfiguration, method implementers should export a getResolver() function which returns an object mapping the method name to a resolve(did: string, parsed: ParsedDID, didResolver: DIDResolver, options: DIDResolutionOptions) function. e.g. { ethr: resolve }.

The resolve function should accept a did string, and an object of type ParsedDID

exportfunctiongetResolver(){asyncfunctionresolve(did: string,parsed: ParsedDID,didResolver: Resolver,options: DIDResolutionOptions): Promise<DIDDocument>{console.log(parsed)// {method: 'mymethod', id: 'abcdefg', did: 'did:mymethod:abcdefg/some/path#fragment=123', path: '/some/path', fragment: 'fragment=123'}constdidDoc= ...//lookupdoc// If you need to lookup another did as part of resolving this did document, the primary DIDResolver object is passed in as wellconstparentDID=awaitdidResolver.resolve(...)// Return the DIDResolutionResult objectreturn{didResolutionMetadata: {contentType: 'application/did+ld+json'},didDocument: didDocdidDocumentMetadata: { ... }}}return{myMethod: resolve}}

The MyMethod getResolver() result could then be passed into the DIDResolver constructor. Note that it should be flattened if used with other methods as well.

import{DIDResolver}from'did-resolver'importMyMethodfrom'mymethod-did-resolver'constmyResolver=MyMethod.getResolver()constresolver=newDIDResolver(myResolver)